He was elected to succeed Joe Hockey as the Liberal Party of Australia member of the House of Representatives seat of North Sydney at the 2015 by-election.

[9] During his time as a councillor, Zimmerman lived openly as a gay man and worked actively on LGBTI issues, describing the de-funding of the NorthAIDS program as "unforgivable".

[9] In the September 2008 Council Elections, Zimmerman ran for the position of Mayor of North Sydney, against the long-serving incumbent, Genia McCaffery who had been in office since 1995.

[19] On 10 February 2022, Zimmerman crossed the floor with four other Liberal MPs to include protection for transgender students in the government's modifications to the Sex Discrimination Act.

[23] Other questions about his preselection were raised since Zimmerman was also the head of the body that sets the rules for party elections, a position his opponents described as a "complete conflict of interest.

[26] In 2018, Zimmerman as Chairman of the Standing Committee on Health, Aged Care and Sport disagreed with the majority view to maintain bans on e-cigarettes.

[27] He subsequently lobbied Greg Hunt, the Government's own Health Minister to delay new restrictions on importing liquid nicotine which is used for vaping.

It subsequently emerged that Zimmerman's coalition partner had received $120,000 from tobacco giant Philip Morris, which has partial ownership of an e-cigarette company.